class RotationalVelocity extends egret.DisplayObjectContainer {
    private arrow:Arrow
    private vr:number = 5

    public constructor() {
        super()
        this.once( egret.Event.ADDED_TO_STAGE, this.onAddToStage, this)
    }

    private onAddToStage(event:egret.Event) {
        this.arrow = new Arrow()
        this.arrow.x = this.stage.stageWidth / 2
        this.arrow.y = this.stage.stageHeight / 2
        this.addChild(this.arrow)

        this.addEventListener(egret.Event.ENTER_FRAME, this.onEnterFrame, this)
    }

    private onEnterFrame(event:egret.Event) {
        this.arrow.rotation += this.vr
    }
}